Preparations of adsorbents having a high affinity for endotoxins in the culture supernatant fluids of Bordetella pertussis were investigated. When poly (gamma-methyl L-glutamate) (PMLG) was used as a matrix and amino groups was used as the ligand, the highest affinity for endotoxin was attained even at high ionic strength (mu=0.2-0.4). PMLG beads. containing amino groups of about 3.2 meq/g selectively removed endotoxin in culture supernatant of B. pertussis without affecting the protective antigens. It was demonstrated that 1 ml of the wet adsorbent adsorbed 4.5 mg of endotoxin. The beads of PMLG derivatives, therefore, are considered to be useful adsorbent for the removal of endotoxin from pertussis vaccine affecting neither filamentous hemagglutinin nor pertussis toxin.